Spectrophotometric Determination of Available Phosphorus in Soil with Bromophenol Blue as an Acid-base Indicator

Standard and common methods for the determination of available phosphorus in soil are usually spectrophotometry methods. Before measurement, the sample is extracted by an acid or base solution, and the pH of the extracted liquid is regulated. The existing methods include complex operation steps such as filtration, and the acid-base indicator dinitrophenol is highly toxic. Most of all, the color of dinitrophenol is easily altered.

To optimize the existing method and improve detection efficiency, and then use the method for soil available state analysis and soil evaluation.

Different experimental conditions such as extraction time, acidity of the extraction and acid-base indicator type were compared. Centrifugal separation was used instead of filtration, and bromophenol blue was first used as the acid-base indicator. Detection results of bromophenol blue and dinitrophenol were compared.

Comparing the detection results of the bromophenol blue indicator and dinitrophenol indicator, the absorbance, accuracy of national standard substance and unknown sample detection results were completely consistent. With bromophenol blue as the acid-base indicator, color mutation was obvious without any interference of bottom color.

Bromophenol blue has low toxicity with accurate detection results. This improved method is appropriate for rapid determination of available phosphorus in acid, neutral and carbonate soils.